Working machines of the type mentioned before are used, for example, for the cutting machining of work pieces, for example in machining centers, machining stations or also in transfer lines. A high degree of machining accuracy is demanded of the working machines mentioned before.
The machining is carried out by machining tools which are set into rotation and positioned by machining spindles. By the cutting machining in the working room chips are whirled around which may be deposited at very different spots.
When a machining tool is changed there is the risk that impurities or chips may get in the spindle head of the machining spindle, between the tool shank and the tool holding device which may still allow clamping the machining tool in the machining spindle, however, interfere with the high machining accuracy which is demanded.
Suggestions have been presented which are supposed to monitor the correct seat of the machining tool on a plane contact surface at the spindle head, and, if the dimensions differ accordingly, prevent machining. Now, the jammed chips and impurities do not interfere with this plane contact, however, these impurities, if they are deposited at the spindle head and not at the plane contact surface, lead to a distinct faulty machining, for example by balance error, and, in the worst case the result of the work piece becomes a reject.
In the state of the art a measuring and monitoring device for the working machines is known where a sensor sensitive for pressure, clamping or force is provided in or under the plane contact surface. This sensor indicates whether the article to be clamped is positioned exactly.